273 Build

-
AJ posted in another thread the effects of CR on small motor
hunt it up

I think this thread post 22 "yet another 273 build advice thread"
Yet another 273 build advice thread!

a later post by me

Kirk at Bullet (662)893-8022 ext 103 reference 620-3
249/ 254 201/206 432 lift 112 in at 107 (+5) uses .858 of the .904 lifter face so it's not out to the edge and should wear well Hyd (or ask about a solid)
that's one size smaller than the 256 Lunati or Howards
how's that look AJ?

my comment on the Bullet suggestion
(IMHO you could also use a single pattern cam with the LCA closed up a little, discuss the tradeoffs)
from what I see the shorter seat allows the Lobe centers to be spread out for the log manifolds and still keep the intake closed point reasonable
longer ex is for the heads and log manifolds
However log manifolds do not like a lot of overlap
btw the chevy version is 400/430 lift this one is much fatter so you still get the power
Bullet has quick turn around when you decide to pull the trigger
you could also check with Jim at racer brown
I do not see a shelf grind that would in any way optimize your build
 
Last edited:
Lee Prim said:
Scratching my head. At 64cc and flat-top I came up with only an 8.3:1 compression ratio. Does that sound right to you ? Sure. It makes for a street engine that can run well on regular gas but it certainly limits power output.
Click to expand...
Sounds about right. With my domed Egge's I measured 9.68/1 static
 
compare the 8:1 and 9:1 and 9.7ish solutions with what AJ posted
I'd start with the 9.68 solution pistons and late heads and open the chambers a little if that too much compression (as opposed to using thick gasket keeping the quench)
the cam Bullet recommended was for sealed power NOS pistons most likely stock or lower than stock compression
YMMV
I asked the poster in that thread for the compression height so we could compare EGGE, domed, and other piston solutions- you might PM him
IMHO most of the book cc's are smaller than reality
CC yours and see which posters have cc's theirs- makes a big difference especially on a small motor
which is much easier to over duration cam than say a 360 or 400
 
Wyrmrider said:
compare the 8:1 and 9:1 and 9.7ish solutions with what AJ posted
I'd start with the 9.68 solution pistons and late heads and open the chambers a little if that too much compression (as opposed to using thick gasket keeping the quench)
the cam Bullet recommended was for sealed power NOS pistons most likely stock or lower than stock compression
YMMV
I asked the poster in that thread for the compression height so we could compare EGGE, domed, and other piston solutions- you might PM him
IMHO most of the book cc's are smaller than reality
CC yours and see which posters have cc's theirs- makes a big difference especially on a small motor
which is much easier to over duration cam than say a 360 or 400
Click to expand...
I read that post on the "Doggyness" of different compression levels. Unfortunately my question was more to gage what I have to work with than what I should be aiming for. The cylinder walls still show the crosshatch marks from the hone and no discernible ridge at the top of its travel so those .040 flat-tops will stay. The heads wont get shaved unless the straight-edge says they need it. I will inquire of the machinist about any budget minded porting tricks he's learned from building engines for round track racers. Not any of that expensive custom hogging out. Wait... This is starting to look like Yet Another Another 273 Build thread that I'll start once we have an idea as to whether we can save these heads or if we shall go straight into a 318 build.
 
I’ll try to take my pistons to the machine shop next week, and get the compression height checked. I don’t have any measuring tools other than a tape measure and framing square! I need to show them to the machinist anyway.
 
I got on Nicks Garage last night on You Tube. It was a live show and he answered my question about a 273. He will be building one in a bit and hopefully doing a video about it. He has done a 273 2 barrel before but probably not on the dyno. He does mostly Mopars. nick's garage - YouTube
 
Richard Sweet said:
Mike or Cliff or …,
For the closed chamber heads that Mike listed in post #202, are there any differences in those heads, other than hardened seats, e.g., are they different for domed pistons vs flat top pistons?
Richard
Click to expand...
302 are 64 cc chamber while the 920 is bigger I believe, like 66 or 67 cc.
302 are induction hardened exh seat but that's not reliable after they cut through the hard surface during the valve job.
I have heads if you need some and can provide them in a few forms, cores, ready to run, and or ported ready to run.
They flow around 175cfm by .500 'stock'
After porting they flow 200cfm by .500 lift. Stock valves still.
 
Last edited:
MOPAROFFICIAL said:
302 are 64 cc chamber while the 920 is bigger I believe, like 66 or 67 cc.
302 are induction hardened exh seat but that's not reliable after they cut through the hard surface during the valve job.
I have heads if you head some and can provide them in a few forms, cores, ready to run, and or ported ready to run.
They flow around 175cfm by .500 'stock'
After porting they flow 200cfm by .500 lift. Stock valves still.
Click to expand...
I updated the chart on page #202 with information from Galen's parts interchange book and Larry Shepards "How to Hot Rod Small Block Mopar Engines" book. The 302's are listed as 56-65cc and the 920's are at 57-64.5cc.
 
Just a word of caution: I'd never work with the lower chamber size numbers listed... they look to be NHRA minimum numbers, for limiting the chamber size reduction in competition work. Not real factory production numbers, but maybe what they used to come up with the manufacturers' typical 3/4 point optimistic advertised CR's!
 
toolmanmike said:
I updated the chart on page #202 with information from Galen's parts interchange book and Larry Shepards "How to Hot Rod Small Block Mopar Engines" book. The 302's are listed as 56-65cc and the 920's are at 57-64.5cc.
Click to expand...
57 cc?
I don't agree with that information because my 1st hand proves that wrong. Most books are out there with some of the crap printed as fact. Ever see any factory x heads at 64cc? That's the kinda stuff that gets printed.. lol
Just the visual gives it away that the 302 is smaller than the 920 by the 920's lack of the peak/point on the closed part of the chamber. My 302's pulled from off a bone stock 318 were wire wheel cleaned measured 64cc. I checked 315 and they were 66-66.5cc

The 920 heads I have currently had hard seats and a valve job. So while you could say they grew... the exh seat got higher by being replaced and the offset is nil. I measure them later today around noon.
 
MOPAROFFICIAL said:
57 cc?
I don't agree with that information because my 1st hand proves that wrong. Most books are out there with some of the crap printed as fact. Ever see any factory x heads at 64cc? That's the kinda stuff that gets printed.. lol
Just the visual gives it away that the 302 is smaller than the 920 by the 920's lack of the peak/point on the closed part of the chamber. My 302's pulled from off a bone stock 318 were wire wheel cleaned measured 64cc. I checked 315 and they were 66-66.5cc

The 920 heads I have currently had hard seats and a valve job. So while you could say they grew... the exh seat got higher by being replaced and the offset is nil. I measure them later today around noon.
Click to expand...
I have a pair of unmolested 302's in the garage. If I can find my cc plate, maybe I will measure mine sometime in the next few days.
 
MOPAROFFICIAL said:
57 cc?
I don't agree with that information because my 1st hand proves that wrong. Most books are out there with some of the crap printed as fact. Ever see any factory x heads at 64cc? That's the kinda stuff that gets printed.. lol
Just the visual gives it away that the 302 is smaller than the 920 by the 920's lack of the peak/point on the closed part of the chamber. My 302's pulled from off a bone stock 318 were wire wheel cleaned measured 64cc. I checked 315 and they were 66-66.5cc

The 920 heads I have currently had hard seats and a valve job. So while you could say they grew... the exh seat got higher by being replaced and the offset is nil. I measure them later today around noon.
Click to expand...
Agree. Who really knows if they even cc'd all those heads to come up with the specs they posted or just took averages or even oe specs from service manuals. (and we all know how misleading some of that information is) They are what they are and all should be checked to make sure before using them for anything serious.
 
Something happened to one of the heads on my 273 along the way. If I remember correctly, I had a 178 and a 920. The bank that had the 920 had one later model rod bearing in it. Anyway, Woody shaved both heads around .030 to get them to the 57cc minimum. Just a FYI.

11_14_0.jpgcrop.jpg150.jpg


clutch kit 017.jpg
 
I always had virgin unmilled heads from back in the day. For 920 head the largest chamber out of 8 was about 65 cc. It took .040 to get to the NHRA 57.3 minimum chamber size. Polished the rest till they were all the same 57.3 cc chambers. I'll take your numbers for 302 heads.
 
toolmanmike said:
Something happened to one of the heads on my 273 along the way. If I remember correctly, I had a 178 and a 920. The bank that had the 920 had one later model rod bearing in it. Anyway, Woody shaved both heads around .030 to get them to the 57cc minimum. Just a FYI.

View attachment 1715466604

View attachment 1715466605
Click to expand...

If you shape and unshroud the chamber around the valves...you can get them to carry higher in the lift and pick up around 6 cfm cfm or so.

20200107_180627.jpg


20200111_134957.jpg
 
66fs said:
Are these flow numbers for 302 heads?
Click to expand...
675 ,315,178 and 920 all flow pretty much the same, talking 2 cfm diff. Chamber shrouds more on the closed versions..as expected. I can flow the 302's i have again...but nothing makes me believe they flow any different.
 
MOPAROFFICIAL said:
675 ,315,178 and 920 all flow pretty much the same, talking 2 cfm diff. Chamber shrouds more on the closed versions..as expected. I can flow the 302's i have again...but nothing makes me believe they flow any different.
Click to expand...

Thanks, I'm not asking you to do more work. Just asking which heads you were talking about.
 
66fs said:
Thanks, I'm not asking you to do more work. Just asking which heads you were talking about.
Click to expand...
I think there are more differences in 360 castings then 273/318. 360 intake port volumes varied, exhaust port changed 5 times at least. 915,587 air injection , 974 air injection boss raised higher, then the 308 head ex port and return to 915 I take port etc.

318/273, they changed the chamber 3 times, closed, open, closed with a sharp point...ping ping.. jk.
Ports maybe changed once, imo..the early intake is more squarish across the short turn and that's more than likely cruder casting. That's all I noticed, and they still flow the same. Exhaust port got air injection bosses too..except that hurt the 318 because the floor was already raised.
 
toolmanmike said:
I got on Nicks Garage last night on You Tube. It was a live show and he answered my question about a 273. He will be building one in a bit and hopefully doing a video about it. He has done a 273 2 barrel before but probably not on the dyno. He does mostly Mopars. nick's garage - YouTube
Click to expand...
I caught Nicks Garage the other night, when sleep was avoiding me. I watched a 408 dyno, but the killer for me was the 241 dyno test. If you remember, probably not, I have a second car. A 1938 Ford Standard Tudor Sedan, with a 325+ 57 Dodge engine, muchly modified. Schneider cam, bored. .040, and a hand made EFI injection system put together by Fran Olson in North Carolina. So, while a completely different motor, it was interesting watching them dyno a baby small hemi. They did get 160 hp out of it, but then had problems when they were trying for more. Stock was 150 hp, but contrary to what they talked about, I believe that 150 hp was with a two barrel, they were using a Carter carb from the mid 50's. But, what intrigued me, was it sounded like it was still gaining power at 5100, where they shut it down. I remember talking with the people at Schneider Cams when I was figuring out what I needed, and they said 5300 was about the maximum for an early Hemi. It was interesting. I wish that I could see a 325 D-500 hemi done on his dyno.
 
hemisedan said:
I caught Nicks Garage the other night, when sleep was avoiding me. I watched a 408 dyno, but the killer for me was the 241 dyno test. If you remember, probably not, I have a second car. A 1938 Ford Standard Tudor Sedan, with a 325+ 57 Dodge engine, muchly modified. Schneider cam, bored. .040, and a hand made EFI injection system put together by Fran Olson in North Carolina. So, while a completely different motor, it was interesting watching them dyno a baby small hemi. They did get 160 hp out of it, but then had problems when they were trying for more. Stock was 150 hp, but contrary to what they talked about, I believe that 150 hp was with a two barrel, they were using a Carter carb from the mid 50's. But, what intrigued me, was it sounded like it was still gaining power at 5100, where they shut it down. I remember talking with the people at Schneider Cams when I was figuring out what I needed, and they said 5300 was about the maximum for an early Hemi. It was interesting. I wish that I could see a 325 D-500 hemi done on his dyno.
Click to expand...
I saw that 241 run as well. I have one that has gone through a couple floods. The chrome is good but the rest isn't I am sure. LOL

241 red ram.jpg
 
I don't know how those last three photo's got in there, but you do have the little baby hemi there. Yes, I overspent my budget on it. Especially with the EFI. But, Fran does very nice work.
 
You must log in or register to reply here.
-

Back
Top